New Measure = add up table column totals

Hello,

As a visual, I've created a table (Matrix) as follows:

Each table column is a sum of a field values in one column of the dataset (sum of all values in the August column in the data set, etc)

I'd like to create a new measure that would add those values across the table above and add the final column "Total" with the total value.

To be honest, I'd probably know how to add all of them as a new visual and there is this figure available in the dataset but a) I'm just starting with PBI and measures and b) I want to double check the figure accuracy.

Thank you